A number of systems are presently found in the industry which generally fulfill the above described function. Among these are: inclined board elevators composed of parallel lugged chains and rejecting cam systems; large diameter rotating drums with external carrying lugs (both foregoing systems basically accomplish single layering of lumber pieces); cam or air actuated lift arm and feed wheel arrangements which, like the chain elevator and drum systems, are believed to have reached a performance ceiling of about 120 pieces per minute of rough sawn random sized lumber.
While the aforementioned feeding systems have held their place in the industry up to the present times, the need for much higher output is now being felt. In fact, resawing of small sized two-faced cants is commonly carried out at speeds of 400 to 500 FPM (in exceptional cases, feed rates through saws have reached 600 FPM), which leads to the need for cant feeding systems to supply some 60 pieces per minute in eight foot lengths and nearly double that amount in the newly developed four foot lumber market. Since the number of pieces produced in cant resawing is often more than twice that of the original cants, further stages of processing such as end trimming and sorting, require under such conditions, reliable feeding capacities well beyond 200 pieces per minute.